Phosphors, whose emission wavelengths vary depending on the types, find use in a wide variety of industries in accordance with the emission wavelengths.
In the lighting field, for example, white light can be theoretically obtained by mixing phosphors displaying light's three primary colors (red, blue, green). To obtain lighting simulating sun light for use in lighting, it has been desired to develop white light having further higher color-rendering property. Because of this, phosphors are required which can broadly emit light having a color displayed in the middle region of three primary colors of light.
Of the phosphors, what is strongly required at present, is a blue-green light-emitting phosphor, which emits blue-green visible light in the intermediate region between blue and green. Since the blue-green light-emitting phosphor emits blue-green visible light, it is an important phosphor which fills a valley formed between blue and green wavelength regions in the emission spectrum. If the blue-green light-emitting phosphor has a sufficient intensity and half width, it can realize white light (lighting) having further higher color-rendering property and capable of substituting for a blue phosphor.
As the blue-green light-emitting phosphor as mentioned above, a halophosphate phosphor is known, which contains an alkaline earth metal, phosphoric acid, a halogen and europium, as constituent elements. Although the blue-green light-emitting phosphor emits blue-green light, not only brightness and high-temperature property are insufficient but also half width is narrow. Thus, the light-emitting properties of the blue-green light-emitting phosphor had many points to be improved.
To improve the light-emitting properties of such a halophosphate phosphor, it has been proposed to add a large amount of alkaline earth metal, in particular, strontium (Sr) as a constituent element, thereby improving light-emitting properties. For this purpose, various types of phosphors have been suggested.
For example, as a conventional blue-green light-emitting phosphor, a phosphor containing Sr: M (M represent a metal element except Eu and Sr) in a ratio of a:b (a and b satisfy the conditions: a+b≤5 and a≥0.1 or b≥3), is known (see, Patent Literatures 1 and 2).
As another conventional blue-green light-emitting phosphor, a phosphor contains (Sr,Ca) and Ba, wherein a ratio of (Sr,Ca):Ba is defined as a:b (a and b satisfy conditions: a+b=5−x (0.3≤x≤1.2) and 0.12≤b/(a+b)≤0.4), is known (see, Patent Literature 3). As another conventional blue-green light-emitting phosphor, a phosphor containing (Sr,Ca) and Ba in a ratio of a:b (a and b satisfy the conditions: a+b=5−x (0.3≤x≤1.2) and 0.05≤b/(a+b)≤0.6), is known (see, Patent Literature 4).
As another conventional blue-green light-emitting phosphor, a phosphor containing Sr and Ba in a ratio of a:b (a and b satisfy the conditions: a+b=5−x (0.3≤x≤1.2) and 0.1≤b/(a+b)≤0.6), is known (see, Patent Literature 5). As another conventional blue-green light-emitting phosphor, a phosphor containing (Sr,Ca) and Ba in a ratio of a:b (a and b satisfy the conditions: a+b=5−x (0.3≤x≤1.2) and 0.05≤b/(a+b)≤0.6), is known (see Patent Literature 6).